Regulator: United doesn't need to accept mistake fares

The U.S. Department of Transportation will not take action against United for voiding thousands of ultra-low tickets it sold earlier this month, the agency said Monday.

The news comes after a week and a half investigation conducted by the department.

"After a careful review of the matter, including the thousands of submissions from consumers and information from United, the Enforcement Office has decided that it will not take action against United for not honoring the tickets," the regulatory agency said.

"The Office (DOT) is concerned that to obtain the fare, some purchasers had to manipulate the search process on the website in order to force the conversion error to Danish Krone by misrepresenting their billing address country as Denmark when, in fact, Denmark was not their billing address country."

In the past, several airlines including United have honored some "mistake fares."